1. Field of the Invention
The present invention relates to a rotational seal device applicable mainly as a gas turbine end rotor seal having a structure that provides an enhanced sealing performance and facilitates assembly or replacement of the seal portion.
2. Description of the Prior Art
FIG. 8 is a cross sectional side view showing one example of a seal structure of a gas turbine rotor end portion which has been developed by the inventors for use together with a steam cooled system of the rotor. In FIG. 8, numeral 11 designates a rotor comprising an inner rotor 11a and an outer rotor 11b. A cooling medium, or steam 20, is supplied between the inner rotor 11a and the outer rotor 11b via a steam inlet 14. The steam, after having cooled the rotor, passes through the inner rotor 11a and flows out of a steam outlet 15 to be recovered. Numeral 16 designates a bearing portion and a labyrinth seal 13 is provided between the outer rotor 11b and a stator 12 for sealing to prevent the steam from leaking outside.
In the above-mentioned end rotor seal, because the end rotor overhangs beyond the bearing portion 16 as shown in FIG. 8, there is a limitation in a rotor axial directional length of the seal portion by which the seal portion cannot be further elongated. Also, because there is a large difference in the thermal elongation between the rotor side and the stator side, there is also a limitation in the length from this point of view. Due to these limitations, if a steam cooled system is to be used for the rotor, the seal length is limited to about 270 mm at most and if a labyrinth seal is employed therefor, the number of stages (number of fins) is limited to about ten (10).
FIGS. 7(a)-7(b) are an explanatory views showing examples of prior art seal structures applied for the end rotor seal described above, wherein FIG. 7(a) is a double strip seal and FIG. 7(b) is a labyrinth seal. In the double strip seal of FIG. 7(a), there are provided fins 32 on the stator side 31 and fins 34 on the rotor side 33, disposed such that the fins 32 are opposed to the fins 34 with a predetermined clearance C in a rotor radial direction being maintained therebetween and also with a fin to fin pitch P in a rotor axial direction with respect to the fins 32 and the fins 34, respectively. If the double strip seal is used for the end rotor seal of a gas turbine, the length L thereof is about 270 mm as mentioned above and when the pitch P=3 mm, the number of fins is 90, when P=6 mm, the number of fins is 45 and when P=10 mm, the number of fins is 27.
In the labyrinth seal of FIG. 7(b), there are provided fins 42, projection portions 43 and fins 44 on the projection portion 43 on the stator side 41 and projection portions 46 on the rotor side 45, disposed such that the fins 42 are opposed to the projection portions 46 with a predetermined clearance C' in the rotor radial direction being maintained therebetween. If this labyrinth seal is used for the end rotor seal of a gas turbine, because there occurs a thermal elongation of about .+-.20 mm in the rotor axial direction, the number of the fins is limited to about ten (10) due to the arrangement of the fins 44 and the projection portions 46.
FIG. 6 is a detailed cross sectional view showing one example of the end rotor seal portion shown in FIG. 8.
In FIG. 6, the interior of the rotor 11 is made in a double structure, wherein numeral 53 designates an outer cooling passage and numeral 54 designates a central cooling passage. A cooling medium, shown by arrow 20a, which is for example a cooling air or the steam 20, as shown in FIG. 8, is led into the outer cooling passage 53 for cooling of the rotor 11 and, after having been used for the cooling, flows in the central cooling passage 54, as shown by arrow 20b, to flow outside of the rotor 11. There are provided a multiplicity of the fins 34 in the rotor axial direction on a rotor outer circumferential surface so as to form a seal portion of the rotor side.
As a seal portion of the stator side, there are provided a multiplicity of the fins 32 in the rotor axial direction, like the fins 34 on the rotor 11, and the fins 32 are disposed close to the fins 34 in an opposing relationship along a rotor circumferential direction. Thus, a double strip seal is formed by the fins 34 on the rotor side and the fins 32 on the stator side.
The fins 34 on the rotor side, as described above, are formed by cutting the outer circumferential surface of the rotor 11, or are buried fixedly therein if the pitch between the fins is comparatively large, so that the rotor 11 and the fins 34 are made integrally in one unit.
In the present state gas turbine, a large amount of cooling air is introduced in the rotor and the blade continuously and thus, a considerable amount of power is consumed for a compressor or a cooler thereof for producing high pressure air therefor, which is an obstacle in enhancing the gas turbine performance. Also, in the recent combined cycle power plant having an enhanced power generation efficiency due to the use of the combination of a gas turbine and a steam turbine, trials are being conducted so that, in place of using air for cooling the rotor or the blade, a portion of steam from the steam turbine is extracted and led into the rotor or the blade for cooling thereof, but this steam cooled system is still being developed.
The seal structure of the prior art gas turbine rotor is formed in one unit of the rotor and the fins as mentioned above, and in case the fins of the rotor have worn out after long hours of use, it is necessary to change the entire rotor along with the fins. Even if only the fins have worn out and there is nothing unusual in the rotor itself, the rotor must be changed, which is very economically inefficient. Also, in the case where the seal is formed by the fins being buried one by one, a long period of time is required in order to perform the difficult task of replacing the fins.